The invention relates to ink jet heater chips and methods for the production of heater chips for ink jet printers.
Ink jet drop on demand printers are available in two main types, thermal ink jet printers and piezoelectric ink jet printers. The printheads for such printers may be configured as roof-shooters or side-shooters depending on the orientation of the nozzle holes with respect to the actuation devices which cause ink to be ejected through the nozzle holes. Thermal ink jet printers rely on resistive heating elements to heat ink and cause formation of a vapor bubble in an ink chamber adjacent the heating element which urges ink through an orifice toward the print media at an extremely rapid rate. High pressures generated in the ink chamber during the bubble formation and collapse can damage the heating elements during the life of the printhead. Accordingly, ink jet heater chips containing the heating elements as the ink ejection devices are typically fabricated with multiple layers of passivation and protection materials on the resistive heating elements.
As the speed of ink jet printers increases, the frequency of ink ejection by individual heating elements also increases thereby increasing the frequency of mechanical shock experienced by the heating elements. Increasing the thickness or number of protection material layers on the heating elements can increase the life of the printhead, however, the thermal efficiency of the heating elements suffers as the thickness or number of protection layers over the heating element increases. A need exists for ink jet heater chips having increased thermal efficiency and processes for making the heater chips which do not significantly increase printhead fabrication costs.
With regard to the foregoing, the invention provides an ink jet heater chip having improved thermal efficiency and method therefore. The chip is of the type which includes a semiconductor substrate, a first metal resistive layer on the substrate, a second metal conductive layer on a first portion of the resistive layer and on a second portion of the resistive layer defining a heater resistor element between the first and second portions of the resistive layer. A passivation layer having a first thickness defined by a deposition process alone is deposited on the second metal conductive layer and heater resistor element. A cavitation layer is deposited and etched adjacent the passivation layer overlying the heater resistor element and second portion of the resistive layer. A dielectric layer is deposited and etched to provide a dielectric layer having a second thickness overlying the first portion of the resistive layer. An electrical conduit via is etched in the dielectric layer. A third metal conductive layer is deposited and etched adjacent the dielectric layer and in the via for electrical contact with the second metal conductive layer.
In another aspect the invention provides a method for improving the thermal efficiency of ink jet heater chips. The chips are of the type having a semiconductor substrate layer, a first metal resistive layer on the substrate layer, a second metal conductive layer on a first portion of the resistive layer, and the second metal conductive layer on a second portion of the resistive layer thereby defining a heater resistor element between the first and second portions of the resistive layer. The method includes the steps of:
depositing a passivation layer on the heater resistor element and second metal conductive layer;
depositing a cavitation layer on the passivation layer;
etching the cavitation layer to expose a portion of the passivation layer overlying the first portion of the resistive layer;
depositing an inter metal dielectric layer on the cavitation layer and exposed portion of the passivation layer;
removing the dielectric layer over the heater resistor element and overlying the second portion of the resistive layer;
etching a via in the dielectric layer and underlying passivation layer to provide an electrical connection conduit to the second metal conductive layer overlying the first portion of the resistive layer;
depositing a third metal conductive layer in the via, adjacent the dielectric layer and adjacent the cavitation layer; and
removing a portion of the third metal conductive layer overlying the heater resistor element and second portion of the resistive layer to provide a heater chip structure.
An important advantage of the invention is the ability to independently control the thicknesses of the passivation layer and dielectric layer so that the thermal efficiency of the heater resistor can be improved. The invention also enables control of the thickness of a passivation layer overlying a heater resistive element by a deposition process alone thereby avoiding passivation layer thinning steps, such as etching the passivation layer portion overlying the heater resistor element surface. The final thickness of the passivation layer overlying the heater resistor elements according to the invention can thereby be controlled by the deposition process used to provide the passivation layer rather than by a passivation and etch process which may result in variations in the passivation layer thickness from chip to chip. For electrical insulation purposes between conductive metal layers, a dielectric layer is provided by a separate deposition and etching process. The thickness of the separate dielectric layer may vary within wide limits since it does not increase the thermal inefficiency of the resistive heating element as described in more detail below. Use of a thinner passivation layer according to the invention provides a reduction in heater energy of about 20% or more.
For purposes of simplifying the description of the invention, the terms xe2x80x9cpassivation layerxe2x80x9d and xe2x80x9cdielectric layerxe2x80x9d are used throughout. However it will be recognized that the dielectric layer and passivation layer may be provided by the same materials and serve similar purposes of electrically insulating and protecting the materials underlying these layers.